1. Field of the Invention
The present invention is directed to a method for dynamic traffic routing in a communication network.
2. Description of the Prior Art
In a fully interworked, non-hierarchic network with n network nodes, n-2 alternate paths with only 2 path sections exist for every source-destination pair. Given a lopsided loaded network some of the total of the nxc3x97(nxe2x88x921)xc3x97(nxe2x88x922) alternate paths network-wide are under-loaded and other paths are overloaded.
Non-hierarchically organized, line-switching communication networks require dynamic routing that adapts to the traffic load present in the network such that the network throughput is optimized. In particular, lopsided load situations must thereby also be defused by the routing.
As in conventional routing in hierarchic networks, an initial attempt is also made in dynamic routing to set up connections via one or more scheduled paths that are usually direct paths. When this is not possible because, for example, all connecting line bundles of the direct path are completely occupied, the overflow traffic is assigned to alternate paths.
The principal difference between dynamic and conventional routing lies in the selection of the alternate paths. In conventional routing, administratively defined alternate paths are searched for an unoccupied line respective an unoccupied channel in a rigid sequence (xe2x80x9cfixed alternate routingxe2x80x9d). As a result thereof, the routing can only react very unsatisfactorily to unplanned, extraordinary load situations.
In dynamic routing, arising overload traffic is assigned to one or more active alternate paths. This active alternate path or, these active alternate paths are not fixed but are selected according to the respective method for dynamic routing or are even redefined at every call. The advantages of dynamic routing lie in its ruggedness and flexibility in response to lopsided load situations in the network that can arise, for example, due to temporally fluctuating loads (for example, spatially limited, strong traffic volume resulting from, for example, catastrophes) and network degradation (for example, outages of connecting line bundles and outages of switching units). Moreover, uncertainties in the network planning can be compensated better.
Central, status-controlled (dynamic) routing methods are supported on a network-central processor that receives information about the existing, local load situation from the network nodes. Beneficial, under-utilized paths can thus be centrally identified and the network nodes can be correspondingly informed. What is thereby disadvantageous, among other things, is the great outlay for network-central processors, data transmission and additionally required calculating capacity in the network nodes.
Decentralized, status-controlled (dynamic) routing methods are based on the answerback of load conditions of the trunk groups to the originating node of the non-hierarchic (sub-) network. These methods have the disadvantage that the non-standardized interface between the network nodes requires a uniform network (for example, network nodes of only one manufacturer), and also a requirement for high signaling outlay.
Decentralized, event-controlled (dynamic) routing methods can achieve a performance enhancement in that they learn the respective load situation by evaluating all trunks busy events (blocking events). However, a distinction is thereby not made between sporadic blockings (caused by statistical fluctuations of the offered traffic) and nearly complete blocking (caused by lopsided load or partial network overload).
European Application EP 0 696 147 A1 discloses a decentralized, event-controlled method for dynamic traffic routing in a communication network. Since the alternate paths are re-selected given a re-initialization and there is no status information in the selection, it is possible in this method that alternate paths that are blocked long-term can be re-activated. Given these re-activated alternate paths, it is therefore determined either already at the first call or at least after a few calls, given a renewed offering of calls, that the alternate path is no longer available and that it must therefore be removed again from the path fan.
An object of the present invention is to avoid the above-identified disadvantages in the prior art. Another object of the present invention is to provide a method of uniformly distributing overflow traffic onto optimally low-occupancy alternate routes better than hitherto.
This object is achieved in accordance with the invention in a method in which highly loaded alternate paths are not as quickly re-introduced into the path fans as less loaded alternate paths.